Red phosphorus in mainly amorphous form may be prepared in a batch procedure by heating white phosphorus in a substantially inert atmosphere above the temperature at which white phosphorus converts to the red form at a practical rate, typically to about 250.degree. C. This procedure has many drawbacks, typically of an environmental nature arising from incomplete conversion of white phosphorus to red phosphorus. Thus, toxic phosphorus fumes may be emitted on opening the reactor, removal of the residual white phosphorus, typically by addition of soda ash followed by leaching produces a phosphate solution requiring disposal, and the disintegration of the red phosphorus product for removal from the reactor by chipping leads to dust formation and hazards to operators.
Attempts have been made to improve upon this prior art operation mainly centered around improving the degree of conversion of white to red phosphorus. Such attempts either have ended in failure or are extremely tedious to execute. One example is the process described in U.s. Pat. No. 3,207,583, wherein extensive heating times and elaborate temperature controls are required.
The prior art procedure just described does not employ any solvent for the phosphorus during the conversion step and no conversion catalysts are added. Procedures are known for the formation of red phosphorus from white phosphorus using such materials. For example, U.S. Pat. No. 804,555 and German Pat. No. 247,905 describe procedures wherein white phosphorus is dissolved in a solvent and red phosphorus is formed in and deposits from the solution phase in the presence of a conversion catalyst for the reaction.
In the prior art, it has also been suggested to form red phosphorus from white phosphorus on a continuous basis. U.S. Pat. No. 2,397,951 describes such a continuous procedure wherein white phosphorus is continuously fed into a converter heated to the desired conversion temperature and containing a substantially fixed volume of a fluid mixture of solid red phosphorus suspended in liquid white phosphorus, the fluid mixture is continuously removed from the converter, red phosphorus separated from liquid white phosphorus and unreacted white phosphorus recycled to the converter.
U.S. Pat. No. 3,998,931 describes an agitated reactor for effecting this continuous process while preventing the build up of red phosphorus solids in the reactor. The reaction is effected in the presence of an inert atmosphere in contact with the fluid mixture in the reactor.